In automotive control applications, it is frequently desired to measure the pressure of certain fluids, such as engine crankcase oil, brake fluid, engine fuel, etc. In general, the best results have been achieved with so-called "backside-sensing" designs in which the fluid to be sensed enters a sealed cavity terminated by the back (inboard) face of the sensor element. The remainder of the cavity is defined by the interior walls of a pressure port which attaches to a wall of the fluid container by a threaded fitting, or the like. The electrical terminals of the sensor element are formed on its front (outboard) face, and may be conveniently coupled to suitable interface circuitry by wire-bonding, for example. In high pressure applications, the sensor element and port are typically formed of stainless steel, and the sensor is welded to the pressure port, forming a hermetic and leak-proof seal between the fluid and the sensor housing. In lower pressure applications, a lower cost silicon sensor may be used; in this case the pressure port may also be formed with a lower cost material, and the sensor can be bonded to the pressure port with a suitable adhesive, which also seals the fluid from the sensor housing.
Clearly, the silicon approach enables significant cost savings compared to the stainless steel approach due to lower cost materials and processing. However, there is some concern about the long term integrity of the seal provided by the adhesive joint between the sensor and pressure port, since the sensed fluid pressure applies tension to the joint. Accordingly, what is needed is a low cost back-side sensor assembly having a durable and high integrity seal between the sensor and pressure port.